This application relates generally to magnetic disc drives and more particularly to a voice coil motor assembly that is partially integrated with the top cover of a disc drive.
Disc drives are data storage devices that store digital data in magnetic form on a rotating storage medium, such as a disc. Modern disc drives include a head disc assembly comprising one or more rigid discs that are coated with a magnetizable medium and mounted on the hub of a drive motor for rotation at a constant high speed. Disc drive components within the head disc assembly, such as the hub of the drive motor, a flex assembly, and a voice coil motor, are mounted to a base plate. A top cover mounts on the base plate to internally seal the head disc assembly. Information is stored on the discs in a plurality of concentric circular tracks typically by an array of transducers (xe2x80x9cheadsxe2x80x9d) mounted to a radial actuator arm (E-block) for movement of the heads relative to the discs. The read/write transducer, e.g. a magneto resistive read/write head, is used to transfer data between a desired track and an external environment. During a write operation, data is written onto the disc track and during a read operation the head senses the data previously written on the disc track and transfers the information to the external environment.
The actuators employ a voice coil motor assembly to position the heads with respect to the disc surfaces. The voice coil motor assembly includes a coil and a magnetic circuit comprising one or more permanent magnet sets and magnetically permeable pole pieces. The coil is mounted on the side of the actuator arm opposite the head arms so as to be immersed in the magnetic field of the magnetic circuit. When controlled direct current (DC) is passed through the coil, an electromagnetic field is set up which interacts with the magnetic field of the magnetic circuit to cause the coil to move in accordance with the well-known Lorentz relationship. As the coil moves, the actuator body pivots about the pivot shaft and the heads move across the disc surfaces.
The heads are mounted via flexures at the ends of a plurality of actuator arms that project radially outward from the actuator body. The actuator body pivots about a bearing assembly mounted on the base plate at a position closely adjacent to the outer extreme of the discs. The head(s) read data and transfer it along the actuator arm to a preamplifier that amplifies the signals coming from the heads.
Typically, a magnetically permeable bottom pole is mounted to the base plate and a magnetically permeable top pole is mounted to the base plate via standoffs in spaced relation to the bottom pole and the top cover. The top pole is mounted such that it forms an air gap between the top pole and the top cover. At least one permanent magnet set is positioned between the two poles and attached to either pole. The coil is positioned between the magnet set and the opposite pole.
FIG. 1 shows a head disc assembly of a conventional disc drive 100. The disc drive 100 includes a base plate 102 to which various components of the disc drive 100 are mounted. A top cover 104, shown partially cut away, cooperates with the base 102 to form an internal, sealed environment for the disc drive 100 in a conventional manner. The components include a drive motor 106 which rotates one or more discs 108 at a constant high speed. Information is written to and read from tracks on the discs 108 through the use of an actuator assembly 110, which rotates during a seek operation about a bearing shaft assembly 112 positioned adjacent the discs 108. The actuator assembly 110 includes a plurality of actuator arms 114 which extend towards the discs 108, with one or more flexures 116 extending from each of the actuator arms 114. Mounted at the distal end of each of the flexures 116 is a head 118 which includes an air bearing slider enabling the head 118 to fly in close proximity above the corresponding surface of the associated disc 108.
During a seek operation, the track position of the heads 118 is controlled through the use of a voice coil motor (VCM) assembly 120, which typically includes a coil 126 attached to the actuator arm 114, a top pole 122, a bottom pole 124 (shown in FIG. 2), and one or more permanent magnet sets 128 having a pair of magnets 129 and 131 with opposite polarity lying in a common plane which establish a magnetic field in which the coil 126 is immersed. The magnet could also be (rather than two pieces) a single part with a transition zone between the two faces of opposite polarity. The top pole 122 is attached in spaced relation to the bottom pole 124 with magnetically permeable standoffs 150. The controlled application of current to the coil 126 causes magnetic interaction between the permanent magnet sets 128 and the coil 126 so that the coil 126 moves in accordance with the well known Lorentz relationship. The top pole 122 and the bottom pole 124 provide a return path for the magnetic field passing through the coil 126. As the coil 126 moves, the actuator assembly 110 pivots about the bearing shaft assembly 112, and the heads 118 are caused to move across the surfaces of the discs 108.
FIG. 2 shows a sectional view of a conventional voice coil motor 120 along line 2-2 of FIG. 1. The bottom pole 124 is mounted to the base plate 102 by any conventional method, such as screws or adhesive. The top pole 122 is mounted to the base plate 102 via standoffs (not shown) such that the top pole 122 is spaced apart from the bottom pole 124. The top pole 122 and the top cover 104 typically form an air gap 123 therebetween. A permanent magnet set 128 is attached to the top pole 122 opposite the top cover 104. The coil 126 is attached to the actuator assembly (not shown) and positioned between the magnet set 128 and the bottom pole 124. An air gap 125 is formed between the magnet set 128 and the coil 126. Another air gap 127 is formed between the coil 126 and the bottom pole 124. One of the problems with this conventional design is that the overall height and size of the disc drive is increased because of the extra space created by the air gap 123. In order to eliminate the air gap 123, the top pole 122 must be adjacent to the top cover 104 and the magnet set 128. A second problem with this conventional design is that it requires unnecessary parts, such as standoffs 150, to mount the top pole 122 within the head disc assembly.
However, this conventional voice coil motor design has several potential areas for improvement. First, this design wastes space because the air gap between the top cover and the top pole is not required in order for the voice coil motor to function. One way to eliminate the air gap would be to mount the top pole directly to an inside surface of the top cover with an adhesive. However, adhesives may cause outgasing that can corrupt normal disc drive operation. A second way to eliminate the air gap would be to weld the top pole directly to the top cover, providing the two parts (cover and pole) are of similar materials and are able to be welded. The problem with welding is that the potential exists for a gap to form between the two parts. The gap may allow contaminates to be trapped and possibly escape to the interior of the head disc assembly. Contaminants that can be trapped even from a cleaning process. Another way to eliminate the air gap and save space is to create a recess in the top cover with an opening into the head disc assembly. The top pole is then mounted to an outside surface of the top cover and the magnet set is inserted into the head disc assembly via the opening in the recess. While this approach saves space by eliminating the air gap between the top pole and the top cover, the opening breaks the seal between the top cover and the base plate thereby increasing the possibility of contamination within the head disc assembly.
A second problem with the conventional voice coil motor design is that it is relatively expensive to manufacture. First, it employs a number of separate parts, such as the standoffs used to mount the top pole, that must be assembled. Second, the poles must be plated to prevent corrosion within the head disc assembly.
Accordingly there is a need for a voice coil motor assembly that saves space but does not corrupt the normal operation of the disc drive. Additionally, there is a need to reduce the manufacturing costs of voice coil motors by eliminating unnecessary parts and manufacturing steps.
Against this backdrop the present invention has been developed. The present invention comprises a voice coil motor assembly in a head disc assembly of a disc drive that is integrated with the top cover of the disc drive thereby reducing the overall size of the disc drive and reducing manufacturing costs associated with the disc drive.
The head disc assembly has a base plate and a top cover enclosing a data storage disc rotatably mounted on a drive motor mounted to the base plate and an actuator arm for transferring data to and from the disc. The voice coil motor comprises a bottom pole, a permanent magnet set, a top pole, and a coil. The bottom pole is attached to the base plate. The permanent magnet set includes a pair of magnets with opposite polarity faces lying in a common plane between the bottom pole and the top cover. The magnet set generates a magnetic field between the bottom pole and the top cover. The top pole rests within a recess in an outer surface of the top cover above the bottom pole and provides a return path for the magnetic field generated by the permanent magnet set. Finally, the voice coil is attached to the actuator arm and positioned within the magnetic field between the bottom pole and the top cover. A second permanent magnet set may be added on an opposite side of the coil from the other permanent magnet set.
These and various other features as well as advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.